Synthesis, Structural Characterization, Photophysics, and Broadband Nonlinear Absorption of a Platinum(II) Complex with the 6‐(7‐Benzothiazol‐2′‐yl‐9,9‐diethyl‐9 H‐fluoren‐2‐yl)‐2,2′‐bipyridinyl Ligand

Abstract

A platinum complex with the 6-(7-benzothiazol-2'-yl-9,9-diethyl-9H-fluoren-2-yl)-2,2'-bipyridinyl ligand (1) was synthesized and the crystal structure was determined. UV/Vis absorption, emission, and transient difference absorption of 1 were systematically investigated. DFT calculations were carried out on 1 to characterize the electronic ground state and aid in the understanding of the nature of low-lying excited electronic states. Complex 1 exhibits intense structured (1)π-π* absorption at λ(abs)<440 nm, and a broad, moderate (1)MLCT/(1)LLCT transition at 440-520 nm in CH(2)Cl(2) solution. A structured (3)π-π*/(3)MLCT emission at about 590 nm was observed at room temperature and at 77 K. Complex 1 exhibits both singlet and triplet excited-state absorption from 450 nm to 750 nm, which are tentatively attributed to the (1)π-π* and (3)π-π* excited states of the 6-(7-benzothiazol-2'-yl-9,9-diethyl-9H-fluoren-2-yl)-2,2'-bipyridine ligand, respectively. Z-scan experiments were conducted by using ns and ps pulses at 532 nm, and ps pulses at a variety of visible and near-IR wavelengths. The experimental data were fitted by a five-level model by using the excited-state parameters obtained from the photophysical study to deduce the effective singlet and triplet excited-state absorption cross sections in the visible spectral region and the effective two-photon absorption cross sections in the near-IR region. Our results demonstrate that 1 possesses large ratios of excited-state absorption cross sections relative to that of the ground-state in the visible spectral region; this results in a remarkable degree of reverse saturable absorption from 1 in CH(2)Cl(2) solution illuminated by ns laser pulses at 532 nm. The two-photon absorption cross sections in the near-IR region for 1 are among the largest values reported for platinum complexes. Therefore, 1 is an excellent, broadband, nonlinear absorbing material that exhibits strong reverse saturable absorption in the visible spectral region and large two-photon-assisted excited-state absorption in the near-IR region.

Cyclometallated tridentate platinum(ii) arylacetylide complexes: old wine in new bottles

“…Sun and coworkers have introduced the electron-donating phenothiazinyl acetylide coligand in 14a and 14b. 46 Both complexes show broadband triplet excited-state absorption. Complex 14b displays a stronger RSA than 14a does due to the smaller ground-state absorption cross-section and larger triplet excited-state absorption at 532 nm for 14b relative to 14a.…”

Luminescent PtII Complexes of Tridentate Cyclometalating 2,5‐Bis(aryl)‐pyridine Ligands

“…[1,2,[4][5][6][7][8][9][10][11][12][13][14] Very soon after their initial use, it was found that many Pt II derivatives of the Phbpy ligand show intense luminescence, some even at ambient temperature. [11,[15][16][17][18][19] One reason lies in the destabilisation of dark metal-centred excited states associ-to 0.44 in PMMA matrices. Detailed electrochemistry (including spectroelectrochemistry) reveals reversible ligand-based first reductions at -2.1 to -2.3 V, irreversible Pt-centred oxidations at around 0.8 V and electrochemical band gaps of 2.8-3.0 eV.…”

Palladium(II) Complexes of Ambidentate and Potentially Cyclometalating 5‐Aryl‐3‐(2′‐pyridyl)‐1,2,4‐triazine Ligands

“…Tridentate cyclometalating ligands, such as the prototypical 6‐phenyl‐2,2′‐bipyridine (HPhbpy) (Scheme ), have been used in organopalladium(II) and ‐platinum(II) chemistry since the 1990s Having the same shape and electron configuration as 2,2′:6′,2′′‐terpyridine (terpy), the anion (Phbpy) – provides very stable tridentate binding, and the cyclometalation requiring C–H activation of the phenyl core can be carried out at moderate conditions, usually heating suitable Pd II or Pt II precursors and the C–H functionalised protoligands (ligand precursor prior to metalation) (Scheme ) . Recently, we came across the interesting class of 5‐aryl‐3‐(2′‐pyridyl)‐1,2,4‐triazines [PyTZ(aryl)] as versatile precursors for HPhbpy derivatives or other highly substituted pyridines (Scheme ) , …”